The installation went smoothly for me. Don’t be surprised if your hard-drive is busy for a about half an hour after you first boot up; that’s Leopard’s Spotlight search program indexing your hard drive.

I want to focus on some of the new features for developers, particularly the upgrade of the Objective-C programming language to version 2.0, and the upgrade of the XCode integrated development environment to version 3.0.

Objective-C is an object-oriented version of C, dating from the early 1980’s, which is a strict super-set of C; that means ordinary C programs will compile successfully under an Objective-C compiler. That makes Objective-C sound a lot like C++, but I like Objective-C a lot more than C++. C++ takes a “Swiss army chainsaw” approach, throwing many new features into the language, while Objective-C is much more minimalist, basically extending the language just to support objects with a Smalltalk-like syntax. Objective-C is also much more dynamic than C++; much more is decided at run-time rather than compile-time. Because of that, it feels a lot closer to programming with a nice scripting language like Python or Ruby. Here’s an excellent introduction to the Objective-C language by Apple; it’s a surprisingly literate piece of technical documentation.

Objective-C is almost never used by itself, instead you use it in conjunction with a set of extensive libraries (the Cocoa libraries on Mac OS X or the GNUstep libraries on Linux or Windows). Cocoa and GNUstep derive from the NeXTStep and OpenStep libraries developed by the NeXT Computer company in the 1980’s and 1990’s. They add both fundamental features (e.g. string handling features, hash tables, that type of thing) and GUI-creation features. These libraries have been under development for 20 years, so they are extraordinarily mature. And since Apple uses Cocoa and Objective-C to develop all of its applications, including Mac OS X itself, it is clear that if you want to develop desktop applications for the Macintosh, you need to learn about them.

I actually believe that using Objective-C and GNUstep is also a very reasonable choice on Linux (or Windows), for those types of applications where you would otherwise use C++, but few people actually make that choice. In fact, I have found that GNUstep and Cocoa are compatible enough that one can pretty easily maintain code that works on all platforms if you need that.

Apple provides a very nice integrated development environment called XCode for free with Mac OS X. If you have not upgraded to Leopard, you’ll be limited to XCode 2.5, while Leopard gives you XCode 3.0. One of the nicest parts of XCode is the “Interface Builder,” which lets you build GUI’s using a GUI instead of by writing code.

With Leopard, Objective-C is being upgraded to version 2.0. Perhaps the most important new feature included is garbage collection. It’s an opt-in system, so legacy code will still work, and you can turn it off if you like allocating and releasing memory yourself, but for new code, most developers will obviously be very happy to have it. This removes one of the major warts of the Objective-C language.

To learn more about building desktop applications for Mac OS X, I highly recommend “Cocoa Programming for Mac OS X” 2nd edition, by Aaron Hillegass. I only wish that there was a third edition that covered the new features of XCode, Objective-C and Cocoa that have appeared in Tiger and Leopard. (UPDATE: Apparently, a 3rd edition is scheduled for Spring 2008.)

If you’re interested in programming Macintosh applications, but prefer to use Ruby, Python, or Haskell instead of Objective-C, you should know about RubyCocoa, PyObjC, and HOC, which let you call the Cocoa libraries from those languages. These tools are very nice, (I’ve actually only used PyObjC personally) but you’ll still need to have some familiarity with Objective-C to understand them.